A wireless local area network (WLAN) is a network that communicatively couples two or more stations over a wireless medium within a limited geographic area. Many WLANs share the wireless medium between stations in the network using a variant of the basic medium access control (MAC) protocol called Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
Using CSMA/CD, a station wanting to gain access to the wireless medium first checks to see if the wireless medium is clear from traffic. If the wireless medium is not clear from traffic, the station waits a random amount of time before retrying to gain access to the wireless medium. If, on the other hand, the wireless medium is clear from traffic, and the station begins transmitting at (or very near) the same time as another station, the two stations' signals will collide. When such a collision occurs, the two stations back off and wait respective amounts of random time before retrying to transmit.
In many WLANs, implementation of the CSMA/CD MAC protocol requires considerable overhead, especially for smaller packet sizes. Several improvements have been suggested to the basic CSMA/CD MAC protocol to reduce overhead and, thereby, increase data throughput. For example, in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 WLANs, techniques such as packet aggregation and reverse direction grants (RDGs) have been introduced to reduce the amount of overhead associated with the CSMA/CD MAC protocol.
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